Mechanical and flame retardant properties of polyethylene terephthalate composites with various structured oligomeric phenyl silsesquioxanes

Structure determines performance. To investigate the impact of POSS structure on the properties of PET, this study employed a melt blending method to incorporate cage-type POSS (OPS), incomplete cage-type POSS (T₇), ladder-like POSS (LPPSQ), and phenyl vinyl ladder-like POSS (VPPSQ) in 5 wt. % into the PET matrix. The effects of different POSS structures on the thermodynamic properties, mechanical properties, and flame retardancy of PET were systematically explored. The results indicate that POSSs exhibits a significant effect on enhancing the flame retardancy of PET. Notably, LPPSQ and T₇ also significantly enhanced the mechanical properties of PET, with T₇ showing the most pronounced effect. Compared to PET, the tensile strength, flexural strength, and impact strength of PET composite with T₇ increased by 29 %, 6 %, and 12 %, respectively. Additionally, its limiting oxygen index (LOI) increased from 20.2 % to 28.2 %, while the peak heat release rate, total heat release, total smoke release, and maximum specific optical density decreased by 56 %, 10 %, 22 %, and 58 %, respectively. In addition, molecular dynamics simulations were employed to investigate the relationship between the structure of POSSs and their compatibility with PET at the molecular level.